In recent years, for example, when performing various processes of, such as a silicon oxide-film formation (film forming) and impurity diffusion in a semiconductor manufacturing process, a work piece is heat-treated, for example, at a high temperature of 900-1200° C. (degrees Celsius) by light emitted from a light source. Especially, a rapid thermal processing (RPT) is used preferably. In the RPT, the temperature of the work piece, such as a semiconductor wafer is raised or lowered quickly, whereby the yield and the quality thereof can be improved. In a light emitting type heat treatment apparatus which performs such a RTP, for example, a filament lamp, in an arc tube of which a filament made of tungsten is arranged, is used as a heat source.
In recent years, for example, in order to reduce an operational voltage (threshold voltage) of a MOS transistor, in a process of formation of NiSi (nickel silicide) film or PdSi (palladium silicide) film, which is used for an electrode of a semiconductor element, it is necessary to heat-treat a semiconductor substrate which is a work piece, at a low temperature, for example, 100-500° C. (degrees Celsius) which is lower than that in the silicon dioxide film formation or impurity diffusion.
In prior art, as a method of forming a metallic silicide film, in general, for example, after forming a film of metal such as nickel (Ni) or palladium (Pd) on a surface of a silicon (Si) substrate by a sputtering method, the Si substrate is heat-treated using an electric furnace, whereby Si and metal are reacted with each other so that a metallic silicide compound is produced. However, when, in a formation of the metallic silicide film, a heat treatment is performed by using such an electric furnace, since the Si substrate is exposed to high temperatures over a long time within the electric furnace, a diffusion layer in a MOS channel deteriorates so that there is a possibility that a semiconductor device may be damaged.
As a means for avoiding damage of the semiconductor device by the above heat treatment, a rapid thermal processing (RTP) may be performed to the Si substrate by using a filament lamp as a heat source.
Moreover, for example, when the surface temperature of a work piece, such as a Si substrate, is uneven, a desired capability which is required for the semiconductor device may not be obtained. When performing the above processes, it is necessary to heat the Si substrate at a constant temperature distribution, without producing local variation in temperature.
However, when a light emitting type heat treatment apparatus in which a filament lamp is provided, is actually used and a heat treatment is performed under temperature conditions in which the surface temperature of the Si substrate becomes approximately 100-500° C. (degrees Celsius), variation in temperature is present in the Si substrate, that is, portions of high temperature and/or low temperature of the Si substrate are locally formed. Thus, there is a problem that it is not possible to heat the Si substrate so as to form a uniform temperature distribution.
This is because in such a rapid thermal processing using a filament lamp, usually, a temperature raising heat treatment for raising the surface temperature of a work piece to a desired heat treatment temperature for a short time of several seconds is performed. After that, a constant temperature heat treatment for heating the work piece for a predetermined time is performed in a state where the temperature of the work piece is maintained at the heat treatment temperature (refer to (a) of FIG. 3). In case where the work piece processed in such a rapid thermal processing is a Si substrate of φ300 mm, in order to raise the surface temperature of the Si substrate quickly at a temperature raising speed of approximately 100 degrees Celsius/second (° C./sec) in the temperature raising heat treatment, a light emitting type heat treatment apparatus to which a large electric power of about 90 kW can be applied as rated power is required. When a constant temperature heat treatment is performed by a filament lamp provided in such a light emitting type heat treatment apparatus, in order to maintain the surface temperature of the Si substrate to a desired temperature, a filament lamp is driven in a state where electric energy supplied to the filament lamp is suppressed to approximately low electric power of 5 kW.
However, in the constant temperature heat treatment, when low electric power of approximately 5 kW is applied to light the filament lamp of the light emitting type heat treatment apparatus whose rated power is 90 kW, the light emission wavelength emitted from the filament lamp shifts to a long wavelength side as shown in FIG. 5, and the radiant intensity of the long wavelength side becomes large. That is, it has turned out that, as the electric power applied becomes low, there is a tendency that the light emission wavelength emitted from the filament lamp shifts to the long wavelength side. This is because, since in the filament lamp of the light emitting type heat treatment apparatus whose rated power is 90 kW, the mass and the surface area of the filament per unit length are designed to be so large that the filament may not be fused even if large electric power is applied, it is thought that when the electric power applied therein is small, the temperature of the filament more remarkably decreases lower than that at time of rated lighting.
On the other hand, it is known that a Si substrate has the light transmission characteristics as shown in (a) of FIG. 6, i.e., a tendency that, as a wavelength thereof is long, a transmittance thereof becomes high (the absorbance becomes low). Moreover, GaAs ((b) of FIG. 6), or Ge ((c) of FIG. 6) has a similar tendency to that of the Si. Therefore, when the lamp is driven by electric power which is sufficiently low, as compared with rated power, as the temperature of the filament decreases lower than that at the time of rated lighting, the light emission wavelength shifts to a long wavelength side, for example, the wavelength shifts to 1.1 micrometers (μm) or more, whereby the Si substrate transmits a great portion of light which is emitted from the filament lamp, without the light being absorbed by the Si substrate.
As mentioned above, in a rapid thermal processing of a Si substrate using a filament lamp, when a constant temperature heat treatment is performed by lighting the filament lamp by electric power sufficiently lower than rated power, the light emitted from the filament lamp is shifted to the long wavelength side which the Si substrate mainly transmits. As shown in FIG. 7, inside the light emitting type heat treatment apparatus in which the filament lamp 60 is accommodated, while the Si substrate which is a work piece W transmits light of the long wavelength side in a state where part of the light is absorbed therein, the light is repeatedly reflected between the reflector 61 located in the opposite side of the filament lamp 60 to the Si substrate, and inner faces of the chamber 65 in which the Si substrate is placed. Therefore, the temperature of the Si substrate is considered to become high or low locally, so that the temperature distribution of the Si substrate does not become uniform. In addition, a reference numeral 62 in FIG. 7 indicates a window member.